1. Field of the Invention
The present invention relates to a zoom lens and in particular to a super wide-angle zoom lens system with a large angle of view.
2. Related Background Art
There have been rare proposals of a super wide-angle zoom lens system compact, composed of a small number of lens elements, and having an angle of view 2ω of 100° or more in an wide-angle end state. As an example, there is Japanese Patent Application Laid-Open No. 2000-2837 owned by the same assignee as the present application. Moreover, a super wide-angle single focal length lens using an aspherical surface suitable to be manufactured by means of a glass molding has been proposed in Japanese Patent Application Laid-Open No. 2001-159732 owned by the same assignee as the present application. Furthermore, a zoom lens using an aspherical lens suitable to be manufactured by means of a glass molding has been proposed in Japanese Patent Application Laid-Open No. 11-287953.
However, there still have needed more study for high optical performance and lowering its cost for those lenses proposed above-described publications, so that a super wide-angle zoom lens system using an aspherical lens corresponding to an easy manufacturing glass molding has been expected.
The major problems of a super wide-angle zoom lens system are such as compactness for regular use, high optical performance, securing a peripheral quantity of light, and productivity of an aspherical lens. In particular, it is important that an aspherical lens to be used can be easily produced by a current mass production technology.
In view of manufacturing method, that an aspherical lens can be manufactured by the glass molding having high productivity not by a precision grinding having low productivity results in cost down, so that there is a large merit for a user. From this point of view, in an optical system disclosed in Japanese Patent Application Laid-Open No. 2000-2837, the aspherical lens is difficult to be manufactured by the glass molding or the precision grinding instead of compound type aspherical surface made of glass and resin, so that the productivity is low. Moreover, a peripheral quantity of light and aberrations are necessary to be improved.
The zoom lens disclosed in Japanese Patent Application Laid-Open No. 11-287953 has a narrow angle of view 2ω of about 64° in the wide-angle end state, and optical performance is not sufficient, so that it is difficult to realize a compact super wide-angle zoom lens system with high optical performance by extending this technology.